US3239635A

US3239635A - Disc shaped arcing contact structure producing predetermined arc blowout characteristic

Info

Publication number: US3239635A
Application number: US412599A
Authority: US
Inventors: Baude John
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-11-17
Filing date: 1964-11-17
Publication date: 1966-03-08
Anticipated expiration: 1983-03-08

Description

March 8, 1966 J. BAUDE 3,239,635

DISC SHAPED ARCING CONTACT STRUCTURE PRODUCING PREDETERMINED ARC BLOWOUT CHARACTERISTIC Filed Nov. 17, 1964 QA tO/QM SOPL lo rm. @Zwmde United States Patent 3,239,635 DISC SHAPED ARCING CONTACT STRUCTURE PRODUCING PREDETERMINED ARC BLOW- OUT CHARACTERISTIC John Baude, 7918 W. Lorraine Place, Milwaukee, Wis. Filed Nov. 17, 1964, Ser. No. 412,599 6 Claims. (Cl. 200-144) This application is a continuation-in-part of my copending application Serial No. 204,490, filed June 22, 1962, now abandoned, entitled, Arc Extinguishing Contact Structure for Electric Circuit Interrupter.

This invention relates to circuit interrupters and more particularly to a. contact structure that may be used with circuit interrupters of the vacuum type.

Circuit interrupters of the vacuum type usually employ a pair of separable contacts disposed within a vacuumized envelope. Circuit interruption is initiated by separating these contacts to establish an arc. The are maintains itself until about the time of a current zero after which the arc is prevented from reigniting by the high dielectric strength of the vacuum.

The interrupting capacity of such an interrupter can be materially increased by moving the are at high speed along the surfaces of the contacts. Such movement tends to minimize the amount of metallic vapors generated from the contacts by the arc and tends to increase the degree of diffusion of these vapors. These conditions enable the vacuum to recover its dielectric strength more rapidly after a current zero and renders the vacuum more capable of preventing reestablishment of the arc.

In other nonvacuum types of interrupters high speed movement of the are also facilitates circuit interruption by decreasing contact heating and vaporization thereby increasing the rate of dielectric recovery.

In accordance with the invention claimed a new and improved circuit interrupter is provided that employs a pair of coacting contacts relatively movable from a position of engagement to a position of disengagement to establish a circuit interrupting arc between the arcing contacts. One of the contacts is set forth as comprising a mobile conductive center section and a conductive annular section mounted on and surrounding the contact engaging center section for limited independent movement thereon. The center section and the annular section both engage the other of the arcing contacts in contact engagement position. The conductive annular section is substantially insulated from the center section near the contacting surface when the contacts are in an engaged position. The arcing contacts are so constructed that a new current path is created upon opening of the contact when the center section separates to cause a momentary reversal of the current and create magnetic forces that assist initiating the driving of the arc across the surface onto the outer peripheral region of the contacts.

An object of this invention is to provided a new and improved circuit interrupter.

A further object of this invention is to provide a new and improved vacuum type circuit interrupter employing a contact structure for driving an are at high speeds along its surface.

A further object of this invention is to provide a new and improved contact structure for a vacuum circuit interrupter wherein a movable contact employs a pair of contact members which move independently and sequentially of each other to produce a magnetic field at the instant of contact opening that initiates arc blowout characteristics.

A still further object of this invention is to provide a new and improved vacuum circuit interrupter employing sliding contacts that are capable of being rapidly opened and closed in an energized A.C. circuit without destructive galling or seizure and does not produce excessive current chopping at low currents.

Objects and advantages other than those set forth may be apparent from the following description when read in connection with the accompanying drawing in which:

FIG. 1 is an elevational view partially in axial section of a vacuum switch embodying the invention;

FIG. 2 is an enlarged partial cross sectional view of the contact structure shown in FIG. 1 in an intermediate contact engagement position; and

FIG. 3 is an enlarged partial cross sectional view of the contact structure shown in FIG. 1 with the contacts in contact disengagement position.

Referring more particularly to the drawing by characters of reference, FIG. 1 illustrates an electric switch 5 comprising a cylindrical envelope 6 which may be formed, for example, of a suitable vitreous material. One end of the envelope 6 is provided with an annular rim 7 to which is secured in gas tight connection one end of a ring or flange 8. A metallic cap 9 is sealed throughout its edge to the other end of flange 8 in the manner shown in FIG. 1. Cap 9 may be provided with a venting passage (not shown) through which envelope 6 may be evacuated and sealed in the usual way. Cap 9 supports a contact mounting or bushing 11 to which is secured one end of a fixed contact 12. Contact 12 is arranged to extend along the longitudinal axis of envelope 6 and is substantially rigidly supported so as to restrict longitudinal or lateral movement thereof. A contact surface 13 of fixed contact 12 is provided having a concave surface facing inwardly of cap 9 and toward the other coacting contact 14 which engages therewith.

The opposite end of envelope 6 is provided with an annular rim 15 to which is fixedly secured in a vacuum tight connection one end of a ring or flange 16. The other end of flange 16 is sealed as shown in FIG. 1 to a ringlike bracket 17. The inner periphery of bracket 17 is sealed to a tube 18, which tube is arranged to extend inwardly of envelope 6. A metallic cylindrically shaped bellows 19 is fixedly secured in fluid tight connection to the inner end of ring 18. The other end of bellows 19 surrounds and is fixedly attached in a vacuum tight connection to the movable contact 14.

The relatively movable cooperating arcing

contacts

12 and 14 may be made of any suitable arcing contact material refined to any suitable degree of deionization and crystallization. As shown in FIG. 1, the movable contact 14 comprises a mobile contact center section 21 and a conductive annular section 22 coaxially mounted around center section 21 for limited independent movement. The movable contact engaging surface comprises an annular contact section 23 coax-ially mounted around a contact engaging end 29 of center section 21, and when contact rod 21 is in contact engagement position with contact 12 it substantially but not completely closes the aperture 24 of annular contact section 23 to complete the outline of the contacting surface. Contact end 29 is separated by a small air gap from annular section 23 when the contacts are engaged. The air gap serves to electrically insulate the center section from the annular section. Upon opening of the contacts a current reversal occurs, as shown by line A in FIG. 2, that creates a magnetic field that assists in moving the arc outwardly, as shown by lines A in FIG. 3.

An outwardly extending flange 25 is mounted around the outer periphery of center section 21 at a substantial distance from the contact engaging end thereof and is adapted to provide sufficient pressure between itself and annular section 24 and center section 21 to provide a relatively low resistance path therebetween. An inwardly extending flange 26- is mounted within a cylindrical portion 22 adjacent annular section 23 and is adapted to provide substantial electrical resistance between flange 26 and annular section 24 because of relatively low contacting pressure. A spring 27 is coaxially arranged around center section 21 between

flanges

25 and 26 for biasing the annular section 23. Center section 21 and cylindrical portion 22 are in sliding engagement with each other and substantially in conductive engagement at flange 25. When the movable contact 14 is in engagement with contact 12 both center section contact engaging end 29 and annular contact surface 23 engage in electrical contact the relatively stationary contact 12.

Annular section 23 has its entire concave surface 28 facing contact 12. Due to the particular construction of the contact surface an are emitted upon separation of

contacts

12 and 14 is established at a point inwardly spaced from the outer peripheral region of

contact surfaces

13 and 28 and is driven by the magnetic forces of the arc across the major surfaces of the disk shaped members to their outer periphery thereof as shown in FIG. 3.

As shown in FIG. 1, when current flows through the movable and stationary arcing contacts in contact engaged position it follows in a parallel path simultaneously through center section 21, flange 25, and annular section 23 to contact 12. After a predetermined travel of center section 21 the flange portion of contact engaging end 29 engages the top of flange 26 at sufiicient pressure to create a low resistance path between flange 26 and the flange of contact end 29 that changes current direction and creates a magnetic force for initiating the outward movement of the extinguishing arc. Also the flange of end 29 actuates cylindrical portion 22 to move it in contact opening direction. Upon separation of the

contact surfaces

13 and 23 the arc is initiated at the point of current path illustrated in FIG. 2 by the arrow. This point is inwardly spaced from the outer peripheral region of the disk shaped members. At the point of separation of surface 29 from surface 13 the arc begins to be affected by an outwardly driving magnetic force and upon separation of

contact surfaces

13 and 23 the arc is therefore quickly driven in a radial direction toward the outer periphery of the surfaces as a result of the initiating magnetic effect of loop circuit A shown in FIG. 2. Such movement of the arc is advantageous in that it lessens the amount of contact material that will be vaporized by the arc and also increases the degree of diffusion of the vapors that are generated. This enables the vacuum to recover its dielectric strength at an increased rate and thereby improves its ability to prevent reestablishment of the are after a current zero, thus increasing the interrupting capacity of the interrupter.

In order to control the arcing products emitted upon separation of the engaging surfaces of contacts 12 and 14 a cylindrical cup shaped tube or shield 30 is provided around and spaced from contact 12. Shield 30 is arranged to extend beyond the adjacent ends of the

contacts

12 and 14 so as to surround at least a part of contact 14 when in contact engaging position. Shield 30 may be formed of glass or any suitable metallic or nonmetallic material.

As readily noted from the figures of the drawing upon actuation of movable contact 14 in axial contact engaging and contact disengaging directions bellows 19 deflects allowing restricted longitudinal movement of contact 14. Since normal atmospheric pressure tends to expand the bellows into envelope 6, the atmospheric pressure may be utilized to hold the contacts together in normal position or to speedily close the gap between them upon release of an externally applied contact separating force.

It is an important advantage of the claimed contact arrangement that are erosion is substantially reduced. This occurs, if at all, in the regions which are remote from the actual major contact making area between contact surfaces 13 and 29. Since the arc is quickly driven from the end of surface 29 and onto the outer periphery of Contact surface 28 where it remains until extinguished, no substantial arc erosion occurs in the area of major contact engagement of center section 21. With the contact making area of center section 21 unimpaired the usual contact closing pressures as well as the current can be evenly distributed about the contacts to minimize contact welding. Further the disclosed contact arrangement lends itself readily to the establishing of a symmetrical electric field in the region of the arcing gap, i.e., a field which is generally symmetrical with respect to a reference plane which bisects the arcing gap between the fully open contacts and extends perpendicular to the longitudinal axes of the

contacts

12 and 14. This symmetry follows from the fact that the disclosed contacts are of the same general shape and are disposed generally and symmetrically with respect to such a reference plane. The more nonsymmetrical is the electric field in the region of the gap the more pronounced is the polarity eifect around the arcing contacts when subjected to voltages of different and opposite polarity. By employing contact structures of given symmetry this condition is reduced.

One difiiculty encountered in vacuum switch interruption is the tendency to chop, i.e., to force the current flowing through the arc abruptly and prematurely to zero before a natural current zero is reached. The sudden change in current which accompanies chopping induces across any device in the circuit a voltage having a magnitude varying directly with the surge impedances of the devices. If the vacuum interrupter is to be used in a circuit with inductive loads the chopping current must be held to a very low value if the generation of excessive overvoltages is to be avoided.

To overcome the chopping problem the disclosed movable contact structure has been provided wherein the center section separates first from the stationary contact to create a change in current path and initiate magnetic force and then its disk shaped movable head separates from the stationary contact. Because of the concave surface of the disk shaped

surfaces

13 and 28 and the looped current path A shown in FIG. 2, the instantaneous arc length is a function of current magnitude, magnetic field, and are position on the surface of the contacts and thus the chopping problem is overcome. If the rate of charge of the angle B shown in FIG. 2 is too great as compared with the prevailing electromagnetic force of the are which tends to drive the arc to the periphery of the surfaces, chopping will occur similarly to what has been observed with the use of butt shaped contacts. If the rate of charge of angle B is too small as compared with the electromagnetic force of the arc a tendency to sustain the arc duration beyond practical limits will avoid chopping but at the expense of the life of the contacts. Between the two extreme cases can be found the most suitable contact curvature providing for both features, namely avoiding chopping and sustaining contact life. To increase the operative effect of the particular contact structure disclosed the contact material in the region of arcing may be formed of dissimilar material known in the art to lessen welding therebetween. For example, one of

contacts

12 and 14 may be of a silver-cadmium combination while the other one may be of iron. Another combination would be one contact of an iron-bismuth combination while the other one may be of silver.

In describing the invention, the preferred embodiment has been shown and described, but it is obvious to one skilled in the art that there are many variations, combinations, alterations and modifications that may be made without departing from the spirit of the invention, or from the scope of the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electric circuit interrupter comprising:

a first disk shaped contact having a conductive surface with a central portion and a peripheral portion; and

a second disk shaped contact having a conductive surface facing the first contact surface with a central portion and a peripheral portion, said central portion of the contacts contacting each other when the contacts are in an engaged position and said peripheral portions bent away from each other at an angle selected to provide predetermined arc blowout characteristics, said second contact movable from a contact engaging position to a contact disengaging position relative to the first contact to establish a circuit interrupting are between said contacts,

said second contact comprising a center section and an outer annular section surrounding and electrically insulated from said center section near the contacting surfaces with both of said sections in contact with the first contact when the contacts are in an engaged position, said sections connected to have a limited movement relative to each other to effect disengagement of the center section prior to disengagement of the annular section from the first contact upon movement of the second contact in a contact disengaging direction, and said sections electrically interconnected at a point relatively distant from the contacting surfaces to both carry current and contacting each other upon movement of the center section at points relatively near the contacting surfaces selected to produce a momentary change in current direction upon disengagement of the center section to provide a magnetic field for initiating movement of the interrupting are outwardly from the central portion toward the peripheral portion of the contacts.

An electric circuit interrupter comprising:

a second disk shaped contact having a conductive surface facing the first contact surface with a central portion and a peripheral portion, said central portion of the contacts contacting each other when the contacts are in an engaged position and said peripheral portions bent away from each other at an angle selected to provide predetermined arc blowout characteristics, said second contact movable from a contact engaging position to a contact disengaging position relative to the first contact to establish a circuit interrupting arc between said contacts,

said second contact comprising a center section and an outer annular section surrounding and electrically insulated from said center section near the contacting surfaces with both of said sections in contact with the first contact when the contacts are in an engaged position, said sections connectetd to have a limited movement relative to each other to effect disengagement of the center section prior to disengagement of the annular section from the first contact upon movement of the second contact in a contact disengaging direction, and said sections electrically interconnected at a point relatively distant from the contacting surfaces to both carry current through the contact surface when the contacts are in an engaged position and said center section contacting the annular section upon movement of the center section to move the annular section in a contact disengaging direction with said contact between the two sections occurring at points relatively near the contacting surfaces selected to provide a current path for producing a momentary substantial reversal of current direction to produce a magnetic field for initiating movement of the interrupting arc outwardly from the central portion toward the peripheral portion of the contacts.

An electric circuit interrupter comprising:

a first disk shaped contact having a conductive surface with a flat central portion and a peripheral portion; and

a second disk shaped contact having a conductive surface facing the first contact surface with a flat central portion parallel to the flat portion of the first contact and a peripheral portion, said peripheral portions bent away from each other at an angle selected to provide predetermined arc blowout characteristics, said second contact axially movable along a line perpendicular to the plane of the fiat portions of the contacts from a contact engaging position to contact disengaging position relative to the first contact to establish a circuit interrupting are between said contacts,

said second contact comprising .a center section and an outer annular section surrounding and electrically insulated from said center section adjacent the contacting surfaces with both of said sections in contact with the first contact when the contacts are in an engaged position, and said center section contacting the annular section upon movement in a disengaging direction to effect subsequent disengaging movement of the annular section in a contact disengaging direction with said contact between the two sections occurring at points relatively near the contacting surfaces selected to provide a new current path for creating a change in current direction that produces a magnetic field for initiating movement of the interrupting arc outwardly from the central portion toward the peripheral portion of the contacts.

An electric circuit intetrrupter comprising:

a first disk shaped contact having a conductive surface with a fiat central portion and a peripheral portion; and

a second disk shaped contact having a conductive surface facing the first contact surface with a flat central portion parallel to the fiat portion of the first contact and a peripheral portion, said peripheral portions bent away from each other at an angle selected to provide predetermined arc blowout characteristics, said second contact axially movable along a line perpendicular to the plane of the fiat portions of the contacts from a contact engaging position to contact disengaging position relative to the first contact to establish a circuit interrupting arc between said contacts,

said second contact comprising a center section and an outer annular section surrounding and electrically insulated from said center section adjacent the contacting surfaces with both of said sections in contact with the first contact when the contacts are in an engaged position, and said sections connected to have a limited movement relative to each other and interconnected to disengage the center section prior to disengagement of the annular section from the first contact upon movement of the second contact in a contact disengaging direction,

means electrically connecting the sections to each other at points substantially distant from the contact surfaces when the contacts are in the engaged position, and

said sections adapted to electrically contact each other at points near the contact surface upon disengaging movement of the center section with said points selected to provide a new current path for substantially reversing the current direction to produce a magnetic field for initiating movement of the interrupting arc outwardly from the central portion toward the peripheral portion of the contacts.

An electric circuit interrupter comprising:

first disk shaped contact having a generally convex conductive surface with a flat central portion and a curved peripheral portion; and

second disk shaped contact having a generally convex conductive surface facing the first contact surface with a flat central portion parallel to the first contact central portion and a curved peripheral portion having a predetermined angle of curvature relative to the peripheral portion of the first contact, means for electrically interconnecting said sections at said second contact movable along an axis perpenpoints substantially distant from the contact surfaces.

dicular to the plane of the flat portions from a con- 6. A circuit interrupter according to claim 5 wherein tact engaging position to a contact disengaging posisaid means for electrically interconnecting said sections tion relative to the first contact to establish a circuit 5 comprises a second flange circumferentially mounted interrupting arc between said contacts, around the center section in a spaced apart relation to said second contact comprising a cylindrical center the surrounding flange With said second flange in relasection and an outer annular. section surrounding tively low electrical resistance contact with the center and substantially electrically insulated from center section and the annular section.

section along the surrounding'surface With both of 10 said sections in contact with the first contact along References Cited y the Examiner their conductive surfaces when the contacts are in UNITED STATES PATENTS an engaged position,

said center section having a surrounding flange adja- 22? n cent its contact surface and said annular scctlon 15 3,038,980 6/1962 Lee having an inwardly projecting annular flange in cooperating relationship with the surrounding flange FOREIGN PATENTS to be contacted at a surface by the surrounding flange upon movement of the center section in a contact 787,846 12/1957 Great Brltalndisengaging direction to provide a low resistance 20 path at the said surface of contact and to effect KATHLEEN CLAFFY Pnmm'y movement of the annular section in contact disen- BERNARD A. GILHEANY, Examiner. gaging direction, and

Claims

1. AN ELECTRIC CIRCUIT INTERRUPTER COMPRISING: A FIRST DISK SHAPED CONTACT HAVING A CONDUCTIVE SURFACE WITH A CENTRAL PORTION AND A PERIPHERAL PORTION; AND A SECOND DISK SHAPED CONTACT HAVING A CONDUCTIVE SURFACE FACING THE FIRST CONTACT SURFACE WITH A CENTRAL PORTION AND A PERIPHERAL PORTION, SAID CENTRAL PORTION OF THE CONTACTS CONTACTING EACH OTHER WHEN THE CONTACTS ARE IN AN ENGAGED POSITION AND SAID PERIPHERAL PORTIONS BENT AWAY FROM EACH OTHER AT AN ANGLE SELECTED TO PROVIDE PREDETERMINED ARC BLOWOUT CHARACTERISTICS, SAID SECOND CONTACT MOVABLE FROM A CONTACT ENGAGING POSITION TO A CONTACT DISENGAGING POSITION RELATIVE TO THE FIRST CONTACT TO ESTABLISH A CIRCUIT INTERRUPTING ARC BETWEEN SAID CONTACTS, SAID SECOND CONTACT COMPRISING A CENTER SECTION AND AN OUTER ANNULAR SECTION SURROUNDING AND ELECTRICALLY INSULATED FROM SAID CENTER SECTION NEAR THE CONTACTING SURFACES WITH BOTH OF SAID SECTIONS IN CONTACT WITH THE FIRST CONTACT WHEN THE CONTACTS ARE IN AN ENGAGED POSITION, SAID SECTIONS CONNECTED TO HAVE A LIMITED MOVEMENT RELATIVE TO EACH OTHER TO EFFECT DISENGAGEMENT OF THE CENTER SECTION PRIOR TO DISENGAGEMENT OF THE ANNULAR SECTION FROM THE FIRST CONTACT UPON MOVEMENT OF THE SECOND CONTACT IN A CONTACT DISENGAGING DIRECTION, AND SAID SECTIONS ELECTRICALLY INTERCONNECTED AT A POINT RELATIVELY DISTANT FROM THE CONTACTING SURFACES TO BOTH CARRY CURRENT AND CONTACTING EACH OTHER UPON MOVEMENT OF THE CENTER SECTION AT POINTS RELATIVELY NEAR THE CONTACTING SURFACES SELECTED TO PRODUCE A MOMENTARY CHANGE IN CURRENT DIRECTION UPON DISENGAGEMENT OF THE CENTER SECTION TO PROVIDE A MAGNETIC FIELD FOR INITIATING MOVEMENT OF THE INTERRUPTING ARC OUTWARDLY FROM THE CENTRAL PORTION TOWARD THE PERIPHERAL PORTION OF THE CONTACTS.